Traditional speech communication is mainly implemented via PSTN (Public Switch Telephone Network), which actually refers a Phone in common senses, and whose network architecture is as shown in FIG. 1.
With the development of Internet, communication through multimedia computers (PC) is becoming increasingly widespread; therefore, communication between PSTN subscribers and IP network subscribers has been an inevitable requirement. At present, there are two methods to syncretize both PSTN subscribers and IP subscribers.
1, PC to Phone: a telephone number is input at PC, whose software transmits the call to IP phone gateway which then initiates the call to PSTN, till the call finally reaches the called PSTN subscribers. In this manner, switch between IP network and PSTN network is implemented by gateway of the IP phone.
2, ICW (Internet Call Waiting): ICW is mainly used to overcome problems met when a dial-up subscriber receives a call while on-line. In this case, the subscriber should apply and register ICW service at telecom service registry office first. When the subscriber is online, his telephone number and IP address of his computer that is in use will be registered at a ICW service server by his ICW client software; once there is a inbound call to the subscriber, the call will be forwarded automatically to the ICW service server who will initiates the call to the registered IP address via gateway of the IP phone in accordance with the registered call forwarding on busy of ICW service; while the subscriber picks up the phone, communication could begin.
In a system where PSTN subscriber and IP subscriber is snycretized, problems of PC to Phone are easy to solve while the called telephone number can be directly inputted and nothing difficult left; but there will be little more difficulties for Phone to PC mainly because of no identification existing for the PC, even for a dial-up subscriber, his IP address is not fixed either. So it can be seen that the ICW service can merely solve part of the communication problems between PSTN subscribers and PC dial-up subscribers, no solution for communication problems between PSTN subscriber and all the PC subscribers is available.
Neither of the two services described above can provide a simple method to solve the communication problems between PSTN subscriber and PC subscriber; furthermore, there are still additional problems described as follows.
A subscriber may possess several phone numbers which make it difficult to remember and manage, especially a subscriber may use phone at one time, and use PC at another, which brings much troubles in finding him. In addition, various services are independent from each other and may possess their own charging systems, the difficulties in systematic management and payment also trouble the subscriber: when he is going on errands, his telephone number may be different, it will also be a question for other subscribers to find him.